Question

Question #804cf

Answer 1

Because the reaction produces hydrogen gas.

Explanation:

Magnesium metal will react with hydrochloric acid to produce aqueous magnesium chloride, `"MgCl"_2`, and hydrogen gas, `"H"_2`.

`"Mg"_ ((s)) + 2"HCl"_ ((aq)) -> "MgCl"_ (2(aq)) + "H"_ (2(g)) uarr`

The hydrogen gas produced by the reaction will bubble out of the solution--this is what the up arrow added next to `"H"_2` in the balanced chemical equation means--which is what you're seeing when this reaction takes place.

So it's not the magnesium metal itself that fizzles and bubbles, it's the hydrogen gas produced by the reaction.